Karma yoga presents a way of practical living.
It might look apparently straight forward and simple. Yet adopting it is very hard in day to day life. In my experience, key challenges in living by Karma yoga is that setting the right goal, having the strong conviction, retaining the self-belief in hard times and working towards the goal set. It is easier said than done in the face of conflicts of interest that we deal with in everyday life.
In comparison, adoption of Bhakti yoga is much easier. Bhakti is sanskrit word standing for devotion, generally to a specific form of God. Spiritual practice of this devotion is Bhakti yoga. I think, it is best explained by famous words from Bhagavat Gita Sarvaan Dharmaan Parityajya Maam Ekam Saram Vraja. These words are spoken by Lord Krishna. It is a promise from God that you can forget everything else and just come to me. That surrender includes distinction between happiness and sorrow, love and hatred, … even right and wrong
Bhakti yoga, for me, is living with a total trust in God, and total surrender to the will of God.